Transformers amplify and attenuate fluctuating voltages. A transformer is formed with at least two inductors, a primary and a secondary, lying in close proximity (magnetically coupled) to each other. Each inductor consists of a core and a coil wound around the core. When a fluctuating voltage is applied to the coil of the primary inductor, magnetic lines of flux are created in the core of the primary inductor. The magnetic lines of flux permeate the core of the secondary inductor. The changing values of the magnetic lines of flux in the secondary inductor create a time varying current in the secondary coil and hence an induced emf (electromotive force). The induced emf in the secondary coil is directly proportional to the emf in the primary coil and the ratio of the number of turns of the secondary coil to the number of turns of the primary coil.
Typically, inductors have been large and heavy since they were made using a ferromagnetic core to enhance magnetic flux. Recently, inductors have been manufactured on a semiconductor wafer. One such inductor is described in U.S. Pat. No. 3,614,554.